Process for polymerizing tetrafluoroethylene with sulfur chloride pentafluoride and ultraviolet radiation



Unite States This invention relates to a new process for polymerizingtetrafluoroethylene and for making new polymeric compounds containingcarbon, fluorine and splphur.

In US. application Serial No. 806,771, filed April 16, 1959, there isdescribed sulphur chloride pentafluoride SF Cl, and its preparation.

It has .now been discovered that under the influence of ultravioletlight this compound initiates the polymerization of tetrafiuoroethyleneto give, depending on the reaction conditions, polytetrafluoroethylenesof high molecular weight, and new polymeric compounds of relatively lowmolecular weight which are believed to be best described as telomers oftetrafluoroethylene and sulphur chloride pentafluoride.

The new process of the present invention for polymerizingtetrafluoroethylene does not require an aqueous reaction system, andconsequently is an improvement over known methods which require suchsystems and as a result cause corrosion of plant and involve the step ofdrying the polymer. Another advantage of the present process is theability to make polytetrafluoroethylenes of different molecular weightsby varying the proportion of sulphur chloride pentafiuoride added to thetetrafluoroethylene.

According to this invention, there is provided a process forpolymerizing tetrafluoroethylene and for making telomers oftetrafiuoroethylene and sulphur chloride pentafluoride comprisingsubjecting a mixture of tetrafiuoroethylene and sulphur chloridepentafiuoride to the action of ultraviolet light.

The reaction should be carried out in a moisture-free environment but itmay if desired take place in a suitable inert organic solvent. It isconveniently performed at atmospheric pressure but elevated pressures,for example up to several hundred atmospheres, may be used, theirmagnitude being determined by the strength of the polymerizationapparatus which necessarily includes components made of quartz or othermaterials transparent to ultraviolet light.

The reaction is usually carried out at room temperature or below, butelevated temperature, for example up to about 250 C., may be employedprovided means are available to remove the heat of reaction quicklyenough to prevent explosive decompositions occurring.

Ultraviolet radiation of wavelengths below about 3000 A. is thepreferred type, such for example as the emission from low-pressuremercury vapor lamps, which is rich in the 2537 A. line.

The molecular weight of the polymers and telomers of tetrafiuoroethyleneobtained in the process is largely governed by the proportion of sulphurchloride pentafluoride in the reaction mixture. When this proportion issmall, for example in the range 0.1 to 0.001% molar and less, thepolymers are solids with properties substantially indistinguishable frompolytetrailuoroethylene made by known methods. Up to about 3% molarsolids are obtained having softening points above 300 C. but withgreater proportions, lower melting point solids are formed whilst withproportions greater than about 30% molar, mainly liquid products areobtained. It would thus apatent pear that the process can yield a seriesof products ranging from high molecular weight compounds having CP CFchains of such length that the end groups, which presumably are SF and-Cl, are such an insignificant fraction of the molecule as to have nomeasurable effect on its properties, down to relatively low molecularweight compounds having shorter chains whose properties are influencedby the end groups. The high molecular weight compounds for example,exhibit infrared spectra indistinguishable from that of polytetrafluoroethylene made by known methods, but with decreasing molecular weight thecompounds begin to show with increasing intensity at band at Wave numberof 890 cm. and attributed to S-F bonds. It is these lower molecularweight compounds that we have described as telomers; they possess goodthermal stability and include liquids suitable as heat-transfer agentsand greases suitable as lubricants.

In one way of carrying out the process, a silica reaction vessel isconnected to stainless steel filling equipment by means of which thevessel may be pressurized with a mixture of tetrafluoroethylene andsulphur chloride pentafluoride up to a maximum of about 10 atmospheres.The silica vessel is irradiated with a low-pressure mercury vapor lampand polymerization sets'in rapidly, the rate being roughly proportionalto the pressure. The vessel may be repressurized several times withreaction mixture and the polymerization carried on for several hours ifdesired. In the examples below which illustrate but do not restrict thepresent invention, the method of carrying out the process is as above.

Example 1 In an apparatus as described above a mixture oftetrafluoroethylene and sulphur chloride pentafluoride containingapproximately 0.001% molar of the latter was introduced into the silicavessel, which had a volume of about 300 mls., and allowed to react at amaximum pressure of 7 atmospheres and at room temperature for six hours.

A white solid was obtained having a melt viscosity at 440 C. of morethan 10" poises and a sulphur content of less than 0.1% by weight andshowing by infra-red analysis the characteristic bands attributable topolytetrafluoroethylene and no bands at a wave number of 890 emf- At 380C. the weight loss of the solid was 0.0028% Per hour.

Example 2 In a similar experiment to that of Example 1, but with asulphur pentafluoride proportion of approximately 0.01% molar a similarWhite solid was obtained which showed a weight loss at 380 C. of 0.0043%per hour.

Example 3 In a similar experiment to that in Example 1, but with asulphur chloride pentafluoride content of approximately 0.10% molar asimilar white solid was obtained which showed a weight loss of 0.0091%per hour and a very slight indication by infrared analysis of a band ata wave number of 890 cmf Example 4 In a similar experiment to that inExample 1, but with a sulphur chloride pentafluoride proportion ofapproximately 1.0% molar and with a maximum pressure of about 1atmosphere a white solid was obtained showing by infra-red analysis asmall band at a wave number of 890 cm. and having a melting point ofover 400 C. Analysis gave C 23.8%, F 73.6%, CI 1.7% which correspondsroughly to a molecular weight of 2500 assuming one C1 atom per molecule.

In a similar experiment to that in Example 4, but with a sulphurchloride pentafluoride proportion of approximately 3.0% molara whitesolid was obtained which could be separated by hot extraction withcarbon tetrachloride into fractions melting at approximately 315, l50l57and 96110 C. These, respectively, were insoluble in hot carbontetrachloride, precipitated from it on cooling, and left behind onevaporating it. Infrared analysis of the unfractionated material showeda moderate band at a wave number of 890 cmf Analysis gave C 21.5%, F73.0%, C1 3.0% which corresponds roughly to an average molecular weightof 1200.

Example 6, 7 and 8 Melting points of fractions Percent molar SFsCl 1 2 3Degrees Degrees 200-220 130-145 190-205 120-140 liquid products onlyDegrees The present application is a division of U.S. application SerialNo. 840,796, filed September 18, 1959.

What I claim is:

1. A process for polymerizing tetrafluoroethylene comprising subjectinga mixture of tetrafiuoroethylene and at least 0.1% of sulphur chloridepentafluoride to the action of ultraviolet radiation.

2. A process for making solid polymers of tetrafiuoroethylene comprisingsubjecting a mixture of tetrafiuoroethylene and sulphur chloridepentafluoride containing at least 0.1% and less than about 3% molar ofthe latter to the action of ultraviolet radiation.

3. A process for making telomers of tetrafiuoroethylene and sulphurchloride pentafiuoride comprising subjecting a mixture oftetrafluoroethylene and sulphur chloride pentafluoride containing fromabout 3 to 50% molar of the latter to the action of ultravioletradiation.

4. A process as claimed in claim 1 in which the ultraviolet radiation isof wave lengths less than 3000 A.

5. A process as claimed in claim 1 when carried out at elevatedpressures and temperatures.

6. A process as claimed in claim 5 in which the pressure is between 1and 10 atmospheres and the tempera ture between ambient temperature and250 C.

7. A process as claimed in claim 4 in which the ultraviolet radiation inmainly of wave length 2537 A.

References Cited in the file of this patent UNITED STATES PATENTS2,846,472 Tiers Aug. 5, 1958

1. A PROCESS FOR POLYMERIZING TETRAFLUOROETHYLENE COMPRISING SUBJECTINGA MIXTURE OF TETRAFLUOROETHYLENE AND AT LEAST 0.1% OF SULPHUR CHLORIDEPENTAFLUORIDE TO THE ACTION OF ULTRAVIOLET REDIATION.